153. Lust

1. Lust is the vice of indulging in unlawful sexualpleasures.

2. The use of sex is not always lustful or sinful. Thereis a good and virtuous use of sex in marriage, when husband andwife perform their normal and natural function of sex without anyinordinateness (that is, without anything that is in conflict withreason) and, therefore, without employing any unnatural orartificial means of thwarting the natural effect of their action.The only lawful and chaste use of sex is its lawful use inmarriage.

3. Lust consists in disregarding the order and modedictated by reason for the use of sex. Therefore, lust conflictswith reason, and is a sin. The habit of lust is a vice.

4. Lust is listed with the capital sins because many othersins flow from it as from their source.